1. Key Research Institute of Humanities and Social Sciences at Universities of Tianjin, Research Center of Finance and Insurance, Tianjin University of Finance and Economics, Hexi Qu, Tianjin 300222, P. R. China
2. School of Economics, Tianjin University of Finance and Economics, 25 Zhujiang Road, Hexi Qu, Tianjin Shi 300222, P. R. China
3. Institute of Econometrics and Statistics, School of Economics, Nankai University, 94 Weijin Road, Nankai Qu, Tianjin 300071, P. R. China
4. Institute of Economics, School of Economics, Nankai University, Nankai Qu 300071, P. R. China